3D Printing Causing Issues
There is a lot, you can check before printing.

-triangulate faces to make them planar. Go to edit mode select all and triangulate

-check if the normals are as they should be, by turn on face orientation in viewport overlays, any red is a bad sign.

-You can turn on a 3D-print addon where is an option to make manifold, also when in edit mode under mesh>clean up there is a few tools that deal with bad geometry.

-ultimately, which iam using when working with a chaotic and more complicated models, there is an awesome voxel remesh. When you set a right voxel size (by try and error) it makes your model clean for print, but in hight mesh density, so I usually use a decimate modifier after that, to make it more "light" to work with.



In your case, it needs some repairing after the boolean. I went to edit mode selected all and triangulated faces. After that I used 3D-Print add-on and clicked make manifold. it did some cleaning. I think it should print completely fine.



Not all warnings are dangerous for print. Like overhangs, it just informs you that there is a place that needs support. Or zero faces - the size that trigger the “degenerate” test to result in that, if you would select all your mesh (in edit mode) scale it and you’ll see the toolbox will not find any “0 faces”. Problem could be intersecting faces or non-manifold.